The present invention relates to a process for the recovery of zinc and ammonia values from aqueous solutions containing zinc chloride or zinc monoammine chloride and ammonium chloride. It is particularly well suited to the recovery of the zinc and ammonia values from the aqueous by-product streams obtained in the reduction of organochlorine compounds with zinc in the presence of ammonium chloride.
Because of their high cost, the use of zinc metal and zinc chloride as reagents in the manufacture of organic materials is generally feasible only when methods are available to recover the zinc values contained in the aqueous by-product steams produced. Recovery in the form of an aqueous solution of zinc chloride is common since such a solution can be used directly or as a raw material for the production of other zinc compounds. The presence of additional substances, such as ammonium chloride, in by-product streams or other aqueous zinc chloride-containing solutions from which recovery is desired, however, makes the recovery of zinc products in sufficiently pure form to be useful difficult. New, low cost methods of recovery are of great interest. The recovery of ammonia values is also of interest since any ammonia values not recovered represents both a loss of assets and a waste disposal problem.
It has been disclosed in U.S. Pat. 4,500,498 that zinc chloride can be recovered from solutions of zinc chloride in water-immiscible organic solvents containing appropriate extractant agents. This is accomplished by contacting the solutions with an aqueous solution of ammonium chloride and ammonia, separating the organic phase, cooling the aqueous phase, and collecting the zinc diammine chloride that precipitates. The zinc diammine chloride was disclosed to be convertible by pyrolysis to anhydrous zinc chloride and ammonia, both of which can be readily recovered. The aqueous solution remaining after removal of the insolubles was disclosed to be recyclable in the system.